Just for the record, my rims are brand new (~800 km) and clean.
I have a set of KoolStop salmon brake pads (actually 2 sets, .... well, front and rear).

I installed them ~600 km ago and I already had to tighten them (adjust the cable tension) twice in the rear, once in the front.
And looking at the pads, the rear are obviously thinner than they were when new and same in the front (although less noticable).

The efficiency is still very good but is that kind of wear normal? what is the usual lifespan of pads like those?

I heard only good about KoolStop stuff,... so don't think it could come from the very pads.
The installation was done properly too, the pads do not touch the rims at all when brakes are released (~2mm away).

Keep in mind that there's only a very weak correlation between mileage and brake wear. Road miles will wear brakes very little, while city riding or off-road much more.
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Daniel R HicksFeb 18 '13 at 16:30

I had the same pads and they lasted very long, but each time I went into muddy downhill trails, they wore A LOT at once.
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heltonbikerFeb 18 '13 at 20:16

mud is an enemy of any kind of pads, especially v-break pads. Once I had to change perfectly new disk break pads after 40 miles on sandy path in very wet conditions. Tread break pads as consumables.
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trailmaxFeb 19 '13 at 0:37

On the other hand, for more "normal" use (dry paved road only), the same brake pads usually last several years.
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heltonbikerFeb 19 '13 at 1:24

The lifespan of brake pads is not only dependant upon environmental conditions but also very much upon what is put into them.

I'm compelled to point out there is a massive difference between the compounds that manufacturers put into brake pads. I've no idea what compounds are actually in them but I'd describe some as "rubbery", some as "gritty", and many in between.

I've had brake pads that, no matter what I do, will shudder or squeal - I dare say they have too much rubber in them - whilst other pads grind away my rims faster than they wear away themselves. Some work well in the dry and bad in the wet, some the opposite. The optimal compound will depend on where you live.

"Normal" will vary according to your environmental conditions. Rain-Wet is always more wearing on all pads. But my primary point - brake pad compounds do vary wildly. Koolstops might work for some; but not others.

A quiet word on technique: sounds like you don't use the front brake enough... that's where all the stopping power is: weight shifts forward, tire presses down more making more contact with ground, providing more friction with ground, stopping you faster. Favouring the rear brake makes you not slow quickly, squeeze harder, wear more pads, loose traction - all bad. When safe, practice using ALL front brake and no back; do this until you fully appreciate the value of front brake as you enter a corner and learn to transition to back brake only when you're past the apex and sensing trouble - breaking traction with the rear after the apex is recoverable, but on the front, well, can be fatal.

Focus on teaching yourself where in the corner you need that transition - from predominantly front to predominantly rear - to occur.

You will need to constantly tighten up the pads - get to know that adjuster - and maybe even reset the cable once to get the full life of the pads. Rain, no matter what the compound will burn brake pads. If you live in a wet place there's no getting around harsh pads and replacing both the rims and pads often. With factory shimano pads I can need one or two turns after every 20kms in rain and the same only after >200kms when dry. Just tighten the screw till it stops spinning freely then turn back half a turn.

Thx for that! bout the braking technique. When I need to slow down, I mostly use both brakes with more pressure on the front. When I need to stop it is 99% w/ the front brake (and I pull with the rear too, to add some braking power, but it is mostly w/ the front). There are only two situations where I brake only with rear: when I am going quite fast and need to just control my speed and gently lower it: the smaller efficiency and agressivity feels about right. And also when riding downhill on uneven roads w/ lower traction, I brake with the rear because it is safer... Am I braking very wrong??
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tisekFeb 22 '13 at 13:22

1

Maybe a little addition to the transition between front and rear brake while cornering: depending on your speed and the sharpness of the corner, you may need all the traction your tires provide to keep you on track. Therefore you should normally try to not brake at all while you are in the turn. Better brake before the corner to reach a speed that allows you to ride through the corner without having to brake in the corner.
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Benedikt BauerFeb 22 '13 at 20:09

Just to give you a boundary case on how quickly pads can and do wear have a look at my current bike:

I replaced my rear brake pads in Nov 2012. It is now almost March 2013 - so 4 months have passed. My rear brake pad is totally worn and riding metal on metal. I am going to replace it next weekend.

Here are my stats:

4 Months Riding

30 Days/month

1.1 KM commute (each way)

Work 5 days a week

Distance due to commuting: 95 KM

It is possible that I have ridden an equal distance running other errands, but I would think that I am over estimating the "Other distance".

So, Total Distance on a single pair of brake pads: between 100 and 200 KM.

Circumstances making the pads wear out faster:

Winter - The roads are sandy/snowy/slushy and wet. I assume that (despite having fenders) that my pads are getting lots of shit on them. I assume the rims are picking up the crap and dumping it on the pads.

Intersections - I cross three major intersections on the way to work. I (almost) always need to come to a complete stop at these and usually track stand for several minutes until the light changes. I am wondering if locking my back brake during track stands is causing excess wear.

Low quality Pads - I am not sure if I bought cheap pads. Bought them at MEC (Canadian equivalent to REI). They only had one choice in stock.

Lack of maintenance - Rather than cleaning pads or my rims on my beater winter bike, I prefer to do a full bike service once or twice a year. I guess that if I cleaned the pads more frequently they may last longer. I am not convinced however. I think as soon as they hit the road they would be full of salt again. My city loves to layer salt onto the road.

Just to be clear I would expect pads to normally last longer. I am merly saying that it depends on a variaty of factors including: